1. Field of Invention
The present invention relates to the field of well packers, and particularly to a device and method for energizing a well packer seal element.
2. Related Art
Packers are used in oil and gas wells to prevent fluid flow through an annulus formed by a tubing within the well and the wall of the wellbore or casing. The packer is generally integrally connected to the tubing, using, for example, means such as a threaded connection, a ratch-latch assembly, or a J-latch, all of which are well known in the art. The tubing/packer connection generally establishes the seal for the inner radius of the annulus.
The seal for the outer radius of the annulus is generally established by a deformable element such as rubber or an elastomer. A compressive force is generally applied to the deformable element, causing it to extrude radially outward. The element extends from the outer portion of the packer to the wellbore wall or casing and seals between those structures. Sometimes backup rings are used to prevent undesired extrusion in the axial direction. The deformable element may also incorporate other components such as a metallic mesh or garter spring.
Existing seal elements sometimes fail due to differences in thermal expansion properties of the deformable element and the surrounding casing or formation. Generally the rubber or elastomer contracts more in response to a decrease in temperature than does the casing, for example. That can lead to a decrease in contact force and a leak may result.
Another failure mode common in open hole completions involves a long sleeve of rubber that is inflated to produce the necessary contact force to form a seal against the surrounding formation. If pressure is not maintained on the inner wall of the sleeve, the seal is likely to fail.
Another type of packer found in the existing art is the steep pitch helix packer described in U.S. Pat. No. 6,296,054. That packer relies on helical strips that expand radially outward in response to an applied action to produce the desired seal.